Beneficiation of low-grade hematitic ore materials



April 5, 1960 F. D. DE vANEY BENEFICIATION OF LOW-GRADE HEMATITIC OREMATERIALS Filed sept. 25,1958

4 Sheets-Sheet 1 INVENTOR 9704 0'. @LVM Mw, Wb m a ATTORNEY-5 April 5,1960 F. D. DE vANEY BENEFICIATION OF-LOW-GRADE HEMATITIC ORE MATERIALSFiled sept. 25, 1958 4 Sheets-Sheet 2 INVENTOR 4...; ATTORNEYS April 5,1960 F. D. DE vANr-:Y

BENEFICIATION 0F LOW-GRADE HEMATITIC ORE MATERIALS 4 Sheets-Sheet 3Filed Sept. 25, 1958 INVENTOR Aprxl -5, 1960 F. D. DE vANEY 2,931,720

BENEFICIATION oF Low--GRADE HEMATITIC ORE MATERIALS Filed Sept. 25, 19584 Sheets-Sheet 4 6 sm ovm/Ek GAS INVENTOR BY QW/,OWLb/QAM nited StatesPatent C BENEFICIATION OF LOW-GRADE HEMATITIC URE MATERIALS Fred D. DeVaney, Duluth, Minn., assignor to Pickands 5 Claims.v (Cl. 75-35) Thepresent invention relates to the beneticiation of low-grade iron orematerials in which the iron values largely are present as non-magneticoxides (and/or hydroxides), e.g. hematite. The invention is particularlyconcerned with the beneficiation of such iron ore materials in which thenon-magnetic iron mineral is too fine grained to be concentrated bygravity methods of concentration such as sink-oat, tabling, jigging,cyclone or the like.

Heretofore, a few of the cleanest tine-grained, lowgrade, essentiallynon-magnetic iron ore materials in which the predominant iron mineralwas crystalline specularite have been concentrated by a procedureinvolving froth otation. With such materials the dotation process hasbeen relatively successful. However, the majority of lean iron ores areVnon-crystalline and cannot be efectively concentrated by the ilotationprocess.

It has been found that the non-magnetic iron oxide contents of such orematerials lcan -advantageously be concentrated by magnetically roastingthe crushed ore under conditions to convert substantially all-or atleast, the greater part-of the non-magnetic oxidic iron content thereofto magnetite, grinding to tine particle size, and magneticallyseparating the magnetic portion from the non-magnetic tailing.

ln accordance with the general principles of the present invention, themagnetic roasting step is carried out in a generally vertical,shaft-type furnace through which the coarsely crushed ore materialgravitationally descendsdcontinuously, or substantially continuously-asa continuous column in counter flow to a current of a gas mixture havinga net vreducing effect and maintained at a controlled temperature.Said-gas mixture comprises a major amount of carbon dioxide, nitrogen(andother non-oxidizing gaseous components of atmospheric air), and arelatively very smallramount of an active reducing gas of the groupconsisting of hydrogen, carbon monoxide and a mixture of hydrogen andcarbon monoxide.

This general process and apparatus for use in carrying it out have beendisclosed in U.S. Patents Nos. 2,528,552, 2,528,553, and 2,670,946 toPercy H. Royster.

According to the last two mentioned of these patents, substantially allof the gas (i.e., gas mixture) passed in contact with the column of orewas gas which had been, in unheated state, introduced adjacent thebottom of the latter. After a certain amount of counter-current flowthrough the ore column-during which it became heated to some extent byheat transfer from the orea part of this gas stream was diverted fromthe column to a spatially separate mixing chamber wherein the divertedgas was mixed with highly heated, essentially neutral, gaseouscombustion products whereby its temperature was materially elevated, andthe resulting hot mixture was reinf troduced into the ore column-at alevel substantially above the level of diversion-to mingle with theundiverted part of the gas stream and with the latter to traverse theremainder of the ore column. This procedure, and, more particularly, thedisclosed apparatus for Y, 2,931,720 Patented Apr. 5, 1,960

icc

, the furnace included three rather well-defined parts serially'arranged from top to bottom, namely, an uppermost part l-called theheating stove-in which the ore was heated to the selected hightemperatureand at least to some extent reduced; an intermediate part 2called the middle stove-in which the hot ore from part 1 was traversedonly by the aforesaid undivertedportion of the gas stream and in whichreduction was completed (in the event reduction had not already beencompleted in part 1); and a lowermost part 3-called the cooling stove-inwhich the reduced ore was cooled in contact with the freshly introduced,unheated gas stream.v

This three-high procedure was open to two main disadvantages. Firstly,the gas diverted at the top of part- 3 of the furnace to the aforesaidmixing chamber was inherently dust-laden and the entrained dust createdserious problems. Thus, dust carried by the diverted gas tended tosettle out in the flues between furnace part 1 and the mixing chamber,in the mixing chamber itself, and in the ues and ports between themixing chamber and the bottom of part 1 of the reducing furnace, and thebuild-up of such settled-out dust resulted Vin uneven flow of gases fromand to the furnace. Moreover, dust carried into the mixing chambertended to clinker when subjected to the highly heated gaseous combustionproducts, and clinker-formation was distinctly disadvantageous if notactually dangerous. Experience proved that removal `of settled-out dustfrom mixing chambers was a very troublesome procedure. Measures forcounteracting these dust problems were only partially successful.

Secondly, the three-high procedure had the inescapable disadvantage thatthe distribution of the gases which traveled through the furnace properand the amount which was diverted to the mixing chamber varied widely,an exact split being impossible to attain. Such variation in split wasdue to changing pressures (e.g., changing pressures in the intermediatepart 2, of the furnace) and to build-up of settled-out dust in the duesto and from the mixing chamber. For these reasons, the furnace operationwas incapable of close control. For example,A while the temperature ofthe gas leaving the mixing charnber could be maintained constant, itsvolume was not subject to exact control, and hence the total heat inputto part 1 of the furnace varied. Accordingly, the temperature of the gasstream passing through part 1 of the furnace iluctuated because ofvarying percentages of relatively cold undiverted gas mixing with therelatively hot diverted gas.

The process and apparatus of the present invention avoid the abovementioned disadvantages and provide an improved procedure (styled atwo-high procedure) for magnetically roasting the hereinbefore describedore materials. From the standpoint of structure, in the verticalshaft-type furnace per se of the present invention the above referred-tomiddle stove has been omitted entirely, the heating stove being directlyfollowed by the cooling stove, and likewise there has been omitted anyand all flues for diverting partially heated gas from the top of thecooling stove to the mixing chamber. From the standpoint of process thespent gas, after having been cleaned and cooled and otherwiseconditioned, is split into two fractional streams one of which isconducted to the mixing chamber (wherein it is heated to a suitableelevated temperature without significant change in composition, forintroduction into the reducing-furnace at the level of the bottom of theheating stove), and the other of which is-after suitable fortificationwith active reducing gas-conducted to the bottom of the cooling stove.

Specifically, the procedure according to k,the present in- 3 venton iscarried out inthe following manner: intermediate the top and the bottomof the re column there istintroduced into the column and caused to owupwardly through the upper part of the column a current of nou-oxidizingheating gas mixture different in chemical composition from the spent gasmixture which exits f 'rom the top of the ore column but differing fromsuch spent gas in that, as introduced, it is at an elevated ternperatureof the order of from 800 to 1700 F. Simultaneously, there is introducedinto the ore column-at a level adjacent the bottom of the latter-acurrent of a cold (i.e., unheated) reducing gas mixture comprising thegaseous constituents of said spent gas fortified with a small additionof active reducing gas (CO, H2 or a CO--H2 mixture). VThis cold gasmixture, in being forced upwardly through the ore column, reduces anynonmagnetic iron oxide (not already reduced) to Fe3O4, andsimultaneously abstracts heat from the ore thereby cooling the latter,and eventually mingles with the current of heating gas mixture(introduced-as stated above-at a level intermediate the top and thebottom of the column) and in admixture with the latter completes thecountercurrent lpassage through the remainder of the ore column andexits at the top as spent gas.

Because this spent gas still contains some residual active reducing gasvalues, the process is madeessentially cyclic in character, in thefollowing manner: the spent gas, after having been diverted from the topof the furnace, and after having been slightly diminished in volume byventing a few percent to atmosphere-the amount of gas so vented beingequivalent to the gain in volume of the gases in the closed system due(a) to formation of water vapor from the moisture contained in the feedore and (b) to the addition of gaseous products of combustion of fuel inthe mixing chamber-is cooled substantially to room temperature orthereabouts and simultaneously cleaned in a scrubber and then is splitinto two streams of unequal volume. The stream of smaller volume isforced through a mixing chamber wherein it is mixed with a stream ofsubstantially inert, non-oxidizing, hightemperature gas to form theaforesaid heating gas mixture which latter is introduced into the orecolumn adjacent the top and the bottom of the latter. The other,larger-volumed, stream is fortified by admixing with it ay small amountof make-up gas rich in active reducing agent (CO, H2 or mixture thereof)which small amount is sufficient (l) to compensate in volume for thewasted spent gas and (2) to re-formulate the aforesaid current ofreducing gas mixture which is introduced-at'about room temperature-intothe ore column at a level adjacent the bottom of the latter forcountercurrent flow therethrough.

The temperature and volume of the aforesaid heating gas mixture are soadjusted, and the ratio of said heating gas mixture to a unit volume ofcrushed ore material is so maintained, that at the level of introductionof said mixture the ore material is heated to from 800 to' 1700 F. whichtemperature level slopes downwardly to an exit temperature of the spentgas of about 200 F. (or somewhat higher) by reason of heat exchangebetween the hot gases and the ore material particles contacted by saidgases (and which had been charged to the column' at room temperature).

In the process just described, essentially all of the nonmagnetic oxidiciron of the charge column is reduced to Fe304 without, however, furtherreduction to FeO (or, to metallic iron). Prevention of reduction beyondthe magnetite stage, in spite of the high temperature conditionsobtaining in the zone of major reduction, is assured by the presence inthe gases of a relatively very large amount of carbon dioxide gas orwater vapor or a combination of the two. It heretofore had beenconsidered necessary, when reducing with a gas rich in hydrogen, tomaintain a relatively low temperature in order to avoid over-reductionbeyond the FeaO.,I level.

It will be appreciated, from the foregoing description, that the presentinvention avoids some or all of the abovedscussed disadvantages inherentin the operation of a three-high reducing furnace of the vertical shafttype. By not diverting partially heated gas from the furnace per se tothe mixing chamber one eliminates dust from the mixing chamber and fromthe flues and ports leading from the latter to the heating stove part ofthe reducing furnace; likewise, one entirely eliminates any and allvflues leading from the reducing furnace and, hence, en-

tirely avoids material settling problems relative to such flues. Equallyimportant, by the present invention one attains the ability exactly tocontrol the distribution of the gases to the bottom of the cooling stoveand to the mixing chamber in any desired proportion: thereby, theoptimum amount of gas can be distributed to each point. The resultingexact distribution of gas makes it possible much more uniformly tocontrol the temperatures obtaining in the heating stove, both gastemperature and gas volume being subject to close control, and hence tosecure efficient roasting.

As will be appreciated, this procedure is best suited to processing arelatively coarse material-eg., an ore material which has been crushedto l inch-in order to maintain good gas flow and to minimize backpressure. Consequently, for best operation the charge material shouldcontain a minimum of minus 10-14 mesh material. If the crusher productis relatively coarse and does not contain appreciably more than 10% offines (i.e., particles finer than 10-14 mesh), the entire crusherproduct can be charged to the ore column. If, however, the crusherproduct contains larger amounts of the fines, it is expedient either (1)to screen out the fines and to mag` netically roast them by a differentprocess (e.g. by a fluosolids procedures) or (2) to agglomerate them bythe known techniques such as balling, briquet-ting or extruding, and toassociate the resulting pellets or ballad-up masses of fines with theplus 14 mesh fraction being charged to the shaft-type reducing furnace.In this latter connection, I have found that most low-grade startingmaterials contain an appreciable amount (a few percent) of a clay-likeplastic component, and that such component provides a very satisfactorybinder for the fines, thereby making possible a very much simplifiedprocedure for avoiding an unduly high content of fines in the chargecolumn, as follows. Where the starting material (when crushed)inherently produces a substantial amount of the fines but does notcontain an appreciable amount of said clay-like plastic component, Icrush the ore to about 1 inch, pass the entire crusher product through aballing drum (e.g. a balling drum such as that described in my U.S.Patent No. 2,831,210) wherein the finer particles agglomerate into smallballs or pellets-which pellets give the same net effect as do thecoarser pieces of the crusher product-and charge the entire product ofthe balling drum to the ore column of the reducing furnace. This specialprocedure practically avoids the presence of fines in the column, makingfor uniform gas flow with a minimum of back pressure.

On some ores which are essentially rock-like and have little plasticityand, therefore, cannot be balled or extruded, I have found the fines canbe mixed with a small amount of cement--in the order of 5% by weight-andthen briquetted and allowed to set for approximately 48 hours. At theend of this period these briquetted fines have acquired sufficientstrength so that they can be charged along with the natural coarsematerial and little breakage will take place in the passage of thesebriquets through the furnace.

It should be appreciated that it is possible to use, as a 'source ofreducing gas, almost any of the common manufactured gases in which CO orH2 are the principal reducing agents. Natural gas which contains a highpercentage of CH., must be reformed into CO and H2 before it can beeffectively used, It is preferable, however, to

use a gas containing sofe CO rather than all H2 in-orderV t'omaintain afavorable CO2 to CO-l-Hz ratio to prevent formation of FeO in theroasting operation. There is also some advantage in having some CO inthe reducing gas since the reaction of CO+3Fe2O3 2Fe3O4|CO2 isexothermic which tends to maintain furnace temperatures. If onlyhydrogen gas is available the tendency to over-roast to FeO can belargely minimized by introducing water vapor into the entrant gas to thefurnace.'

From the standpoint of the apparatus aspect of the present invention, italready has been mentioned that the reducing furnace is of the shafttype. This shaft may be circular in cross-section, or it may be squareor rectangular in cross-section. For reasons to be discussedhereinafter, it is expedient in many cases so to design the shaftfurnace that its upper part is generally circular, while its lower partis rectangular, in cross-section.

The invention will now be described in greater particularity in thefollowing and in connection with the appended drawing, in which p Fig.11is a schematic representation, in llow sheet form, of apparatusoperable for use in the cyclical reductive roasting process of theinvention;

Fig. 2 is a somewhat enlarged vertical sectional view of a reducingroasting furnace according to the invention, showing a particular formof apparatus for use in contributing heat to the reduction process;

Fig. 3 is similar to Fig. 2, and shows a modified form of reducingfurnace; and

Fig. 4 is a vertical sectional view of a form of reducing furnaceconstruction embodying principles for insuring uniform descent of theore column and for uniform distribution of cooling gas across thecross-sectional area of an ore column resident in the lower part of `thecooling stove.

In Fig. 1, the reducing furnace per se is a substantially vertical shaftcomposed of a lower cooling stove 4 and` an upper heating stove 5.Heating stove 5 is provided at its top with a double bell-and-hopperfeeding means 6 for introducing feed ore into the furnace without lossof gasfrom the system, while cooling stove 4 is provided at its bottomwith a reduced ore product discharge means 3 for positively removingreduced and cooled ore from the reducing furnace, at controllablyvariable rates, without loss of gas from the system. Discharge means 3mayas showninclude a conventional star gate, or it may comprise anyother equivalent discharging device. At 7 there is schematicallyrepresented a wet dust collectorscrubber for cleaning and cooling spentcarrier gas exiting from the top of stove 5 by way of spent gas conduit8. Conduit 8 is provided with a valved vent means 9 for wasting toatmosphere a small (variable) fractional part of the total spent carriergas, and conduit 10 conducts the residual spent carrier gas to scrubber7. In scrubber 7 the carrier gas is cooled (e.g., Ito room temperature,60 F.) and the dust removed and excess moisture condensed out andexpelled together with excess CO2. The so-conditioned carrier gas iswithdrawn from scrubber 7 through conduit 11 by means of blower 12, andby the latter is forced through cold carrier gas conduit 13. Conduit 13delivers to two branch valved conduits 14 and 15 which split the streamof cold clean carrier gas for delivery to inlet conduit 2 and mixingchamber 17, respectively. A conduit 1 delivers active reducing gas,produced in gas producer 18 and cleaned in scrubber 19, to inlet conduit2 for commingling therein with carrier gas to provide an enriched gas.At 16 is indicated a burner means operable for burning fuel oil in acontrolled amount of air to produce hot gaseous combustion productsdevoid of free oxygen, for conuningling in mixing chamber 17 with cleancold carrier gas delivered to mixing chamber 17 through valved conduit15. The hot carrier gas-neutral gaseous combustion products mixtureproduced in chamber 17 is, through conduit 20, introduced into thereducing furnace, at a level adjacent the bottom of heating stove 5, andpasses upwardly-in association with ascending enriched gas (introducedat the bottom of cooling stove 4) with which. latter itcommingles-through that part of the total column of ore resident inheating stove 5. In such passage said-hot carrier gas-neutral gaseouscombustion products mixture gives up a major part of its heat to the orethereby heating the latter to desired reduction temperature. Thev activereducing agent component of the enriched gas, for its part, becomesoxidized (to CO2 or/and H2O, as the case may be) by reaction with theFe203 of the ore, and loses `heat (acquired in passage through the orein stove 4) to the ore in stove 5. 'Ihe commingled gases exit from v thetop of the furnace--through conduit 8-as the aforesaid spent carrier gasthus completing the gas cycle of the process.

Fig. 2 more specifically illustrates one form of furnace adapted for usein carrying out the process and including particular means for producingthe heating gas used forv heating the ore to desired temperature foreffecting reduction of Fe203 to Fe304.

According to this embodiment, the furnace shaft, generally designated30, is composed of, in series, a generally cylindrical uppermost part31; an elongatedmiddle part of which the upper portion 32 has the formof an inverted frustum of a cone and of which the lower portion 33 isgenerally cylindrical and has substantially the same crosssectional areaas that of uppermost part 31 and of the apex end of portion 32; and agenerally conical lowermost part 34. The base end of the frusto-conicalportion 32 has a cross-sectional area larger than that of uppermost part31 and the junction wall 37 joining the open bottom of part 31 with thebase end of portion 32 provides an annular free space 38 between thefurnace Wall and the periphery of a column of ore resident in thefurnace. Parts 31, 32 and 33 are constructed of rebrick backed byheat-insulating material for conserving heat Within the space enclosedby them: part 34 suitably is constructed of sheet metal. p

Junction wall 37 is provided with a plurality of downwardly directedports 40, 40 spaced as closely asjpracticable about the periphery of 37,vwhich ports communicate with an annular chamber 41. Into chamber 41there discharge a pair of conduits 20, 20 from the pair of mixingchambers 17, 17 to be described below. ,j

Conical lowermost part 34 is provided with particular means forintroducing cold enriched gas into the furnace and distributing the samethrough thej cross section of an ore column resident in the furnace. Asshown, inlet conduit 2 discharges into an annular bustle pipe 44 fromwhich latter lead a plurality of valved branch conduits 45, 45, 46, 46.Branch conduits 45, 45 communicate between bustle pipe 44 and theperipheral terminal branches 50, 50 of a gas-distributing means 50, 51,52 centrally disposed within and adjacent the top of lowermost part 34,there being as many branch conduits 45, 45 as there are -terminalbranches 50, 50 (two each being shown in Fig. 2). In saidgas-distributing means, branches 50, 50 extend radially outwardly from acentrally (i.e., axially) disposed multi-louvred gas distributor 51 thelouvres of which are so arranged as to tend to direct gas under pressureradially outwardly therefrom and todistribute the same with substantialuniformity across the cross section of a column of ore particlesresident in the lower part of cooling stove 4. A conical cap piece 52atop of distributor 51 permits the column of ore to pass smoothly overthe distributor. Branches 50, 50 may, if desired, be suitably slotted topermit the discharge of part of the supplied gas therethrough, theresidual part passing to the centrally disposed distributor.

In order to ensure the cooling of the walls of the conical part 34 ofstove 4, a part of the total gas supplied through conduit 2 may, asshown, be diverted through valved branched conduits 46, 46, to anannular chamber 55 surroundingsaid conical part adjacent the baseof'.the cone- At its ylower part'rannular chamber 5.5 merges' into aconical vessel .56 fthe wall of which is .spaced from and generallyparallel .to the Awall f conical part :3 4 thereby providing a gas spacetherebetween vfor downward passage of cool gas (from annular ,cham-ber55) o ver the surface of .part 34. .Conical vessel 56 extendssubstantially beneath the lower edge'34 of conical part 3,4 andterminates in a generally cylindrical discharge tube 6.0 for delivery`of cooled reduced ore from the fur,- nace shaft to a gas-locked productdischarge means in communication withv the open lower en d of said tube.Gas after passing through the space between parts 34 and 56 dischargesat the lower edge 34 into the ore column about the periphery of thelatter.

-,Said gas-locked product discharge means includes a hopper 61 providedwith a gas-tight cover 62 through a central orifice 63 in which covertube 60 extends into the interior of the hopper. A slide valve means 65closes the bottom ofthe hopper and functions to deliver ore particles,from -a constantly maintained `supply thereof in the hopper, to beltconveyor means 66 for the forward: ing of product to a point of use.

In this embodiment of the invention, the heating of thecurrent of coldcarrier gas, provided through valved conduit 15, is effected in an,efficient manner. For thisk purpose, the generally cylindricalcombustion chamber 16 has a diameter smaller than, and is axiallydisposed within, the generally cylindrical mixing chamber 17, therelative sizes of the two chambers being such that an annular space 70is provided between them, into the lower part of'which annular space gasis delivered from 15 to circulate about chamber 16in passing into mixingchamber 17. A burner 72 is axially disposed in the base of combustionchamber 1.6, said burner being supplied with metered (orl otherwisecontrolled) amounts of fuel oil and air through valved oil pipe 73 andvalved primary air pipe 74, respectively, for producing a supply ofhighly heated neutral gaseous combustion products. These latter streamthrough central opening 76 in the top of the combustion chamber and intothe main space within mixing chamber 17 for thorough mixing with thecarrierY gas preheated in passage through annular Space 70.

The mixed gases pass through conduit 2 0 into annular chamber 41.

Onlyr one heating unit has been described above. However, it ispreferred that a pair of identical heating units be employed, the samedelivering hot mixed gas into annular chamber 41 at opposite sides ofthe furnace shaft.

HThe heating units may be constructed somewhat more simply according tothe modification illustrated in Fig. 3. `According to this modification,in each of the pair of heating units the combustion chamber 16 and themixingchamber 17 are series portions of a single horizontally-disposedchamber separated one from the other by a partition wall 80 providedwith a central opening V76 for passage of highly heated gaseouscombustion products from combustion space into mixing space. Carrier gasis led into the latter at an opening 82 in the side wall thereof, forthorough mixing with the heating gas.

In this modified form, cold enriched gas, delivered by conduit `2, isdischarged into the o're column through a hooded discharge member 85.

Ore gravitating through conical lower part 34 passes into the tubularextension 88 and thence into closed vessel 89. This latter is dividedinto upper and lower portions by a generally horizontal aperturedpartition 90 through the apertures o'f which ore particles pass -by theaid of a reciprocatory pusher device 91, 92. A supply of .th oreparticles is maintained in lower part l93,'the bottorn of-which latteris in communication with a star gate 9;,4 of conventional form fordischarge of solids.

4 Fig. 4 illustrates a type o'f furnace peculiarly .well adapted t0handle ,Oresn whiehthere .may be some dini- 8. culty- .inmaterial flow.-In the roasting 4process the .temperatures employed are well below thefusion point `and thus no clinkering occurs. However, with certainores., because of their physical nature and because of the amount ofmoisture or nes present, it is sometimes de.v sirable to incorporate inthe design a series of rotating control shafts whose purpose it is toregulate the descent of the charge. These control shafts serve to breakup any consolidated masses that have been formed-through the packing ofthe material rather than through clinkering ofthe materialand to insurea uniform descent ofthe charge through the furnace which at the sametime. tends to insure a uniform flow of gas up through the shaft of thefurnace.

-In Fig. 4, as in Fig. 2, but one of the pair of identical heating unitshas been illustrated. Also as in Fig. 2,`the" external gas circuit hasvbeen o'mittedV as having already been shown in Fig. l and described inconnection with the latter. i

According to this embodiment, the upper .portion of the furnace shaft ismade circular in cross-section -kthus making it possible to utilize thestructural advantages inherent in a circular design, and permitting theu se 'of a simple double bell-and-hopper device for feeding theore-whilst in the middle portion of the furnace shaft a conversion ismade from a circular to a rectangular' crosssection in order to makepossible the inclusion of a series of horizontally disposed, parallel,rotating breaker shafts in the lower part o'f the cooling chamber orstove 4. Preferably, the conversion is a gradual one, starting from justbelow the level at which the heating gas is introduced into the furnaceand extending to a level above'the bank lof breaker shafts abovementioned.

The breaker shafts extend across the rectangular of the shaft and arejournalled in bearings which are or may be incorporated into' themasonry (brickwork) wall of the shaft, at least one end of each shaftextending exteriorly ofthe wall of the shaft and being provided theexposed end with conventional means (not shown), eg., a connection witha drive rod and crank arm therefor, actuated by a hydraulic cylinder andpiston, fo'r os.- cillating the shaft. In lieu of'such oscillatingmeans, there may be used a rotating means including a drive shaftprovided with a plurality of driving gears cooperating with driven gearskeyed to the exposed ends of the shafts, said drive shaft being roatedby a variable speed motor, preferably of the reversible type. Otherconventional means for o'scillating or rotating the breaker shafts maybe used, it being essential only that said means be adapted to beingactuated at a controlled variable rate of speed. Preferably, theactuation of all of the breaker shafts is effected at one side of thefurnace and by a single actuating means. The breaker shafts areprovided, about that portion of the periphery of each of them which isdispo'sed between the opposite Walls of the shaft, with spacedteeth-arranged either in rows longitudinally and radially of the shaftor helically about the shaftor equivalent protuberances for positivelyaugmenting the downward movement of the ore column.

In this embodiment, the cold (or, cool) enriched gas is introduced, byway of conduit 2, into the ore column by means of a plurality of spaced,parallel, louvered inverted trough-like gas distributors disposedadjacent to but below the bank of breaker shafts and between each pairof adjoining breaker shafts. Thereby, the enriched gas serves to coolthe breaker shafts, and is distributed uniformly over the cross-sectionof the o're column.

As is suggested above, a substantially dry ore of relatively coarsesize, and containing little fines, may not require the assistance of theabove-described breaker shafts in descending substantially evenlythrough the fur nace, in which event the breaker shafts may be dispensedwith: regardless of the exclusion or inclusion of breaker shafts intheorganization, the above-described means of v and downwardly to form,with the shaft wall, an annular plenum space 104V from which heatinggas-supplied through conduit -is forced into the ore column.

A plurality (four illustrated in the drawing) of horizontally disposed,spaced parallel breaker shafts 110, 110 extends across the rectangularpart of stove 4, to the exposed ends 112, 112 of which are attachedconventional means (not shown) for oscillating the breaker shafts. Aboutthe periphery of each breaker shaft is disposed an array of spaced teeth113, 113 Whichwhen the breaker shafts are moved-engage the particles ofthe ore column,

loosen the ore and (their primary function) break up any agglomeratedmasses or chunks o'f material which may have formed. The spacing betweenthe toothed shafts is such that all particles other than said chunksfreely pass between them regardless of whether or not they are beingrotated.

4 Disposed closely beneath breaker shafts 1'10, 110 and parallel withthe latter, are spaced, parallel, inverted trough-like gas distributors(three shown) 120, 120 the' sloping sides of which are louvered (asshown at 121)V to provide an array of gas inlet means making forextensive distribution of gas across the cross-section of therectangular part of stove 4. Gas from conduit 2 enters the trough-likegas distributors by way of branch pipes 122, 1,22 communicating betweenconduit 2 and the interior of members 120, 120. As is illustrated inFig. 4, the number of gas distributors 120, 120 is one less than thenumber of breaker shafts 110, 110,Y and each gas distributor spositioned between (and just beneath) each pair of adjacent breakershafts,Y whereby cool gas is directed onto the breaker shafts and intothe loosened ore particles moving past said shafts and is uniformlydistributed throughout the cross-section of the ore column;

vThe process will now be described in further detail and exemplified bythe following specific examples.

Example` J Theestarting material was a low-grade, siliceoustaconite-like ore from the western Mesabi district, Minnsota- The ironmineral; was largely. hematterbut was too fine grained to beconcentratedbyv oat-sink, jigging or cycloneY methods ofY concentration. "'The orehad the following analysis on a dry basis:

Percent F6203 .0 S102',l 41.5 A1203 1.2

As received, moisture content 6%.

wascharged, at 6, at the rate of 25.44 gross (long) tons per hour, at 60F. g

The blower 12 forced 818.0#/minute of cold, clean, spent carrier gas,delivered to it by conduit 11" from the sesV scrubber 7, through thecold lgas conduit 15, this gas having the following composition:

#/min. Percent oo 7o. 1 s. e CO.. 5. 7 0. 7 Hz- 0. 0 0. 0 H20 14. 8 1. 8N2-- 727. 1 88. 9

Reducing gas used in this example was made from coke in a slagging typegas producer 18, and, after being scrubbed at 19, was forced throughconduit 1, this gas the other portion into conduit 14. The gas inconduit 14 and conduit 15 had the following composition and Volumes:

Conduit 14, #/min.

Percent Conduit 15, #/min.

svt-d3 en Quelqu The carrier gas from conduit 14 and the reducing gasfrom conduit.1 commingled in conduit 2 to produce an enrichedl carriergas ofthe following composition and volume:

#/min. Percent Co, 51.8 7.8 C0.-. 35.3 5.a H2- 0.o 0.o H20 12.0 1.8 N.557.0 85.1

This enriched carrier gas entered the ore column in lower stove 4, whereit recovered heat from the ore, and ascended into the upper ore columnin upper stover 5. As it entered the latter, it commingled with the gasfrom mixing chamber 17.

In mixing chamber 17, 248.5#/min. of gas from conduit 15 was mixed withthe hot (1000 F.) gaseous combustion products, analyzing #/mln Percent Co, 12. 7 21 H20 4. 3 7 Ni Y 43. 5 72 issuing from the combustion chamber16 appurtenant to the mixing chamber, in which combustion chamber fueloil had been burned'with a carefully controlled amount of air so as toproduce a heating gas containing no free XYgeD #/min Percent In order tokeep the system from increasing in pressure, a vent means 9 was providedto keep the system in balance. The minimum top gas Wasted to atmospherewas 12.5%, based on a nitrogen balance. This percentage varied somewhatwith temperature, moisture content, and CO content.

'The remainder of the spent gasesl passed into. a wet dustcollector-scrubber 7 where the same was cooled and the excess moisturecondensed out andexpelled together with the excess CO2 over and beyondthat accumulating in-the system for equilibrium while maintaining anitrogen balance. The volume and composition of these top gases were asfollows:

Percent Of these gases 12.5% were wasted to atmosphere by the vent means(conduit 9) and 87.5% passed to the scrubber (conduit 10).

The heat requirements of the above system were such that 201,000B.t.u./min. were required to heat the ore from 60 F. to 1,000 F.; 67,000B.t.u./min. were required to evaporate 'the moisture to dehydrate theore; and 10,000 B.t.u./min. were necessary to compensate for radiationlosses, for a total of 278,000 B.t.u./min.

The heat sources were: 44,000 B.t.u./min. from the exothermic reaction;160,000 B.t.u./min. were recovered by the ascending gasesand 74,000Btp/min. were supplied by combustion of fuel oil at the combustionchamber. 7 l Y i The heat losses from the reducing furnace were:

Heat in top gases of which 67,000 was for dehydration of ore 227,000

Total 278,000

The ore as fed to the furnace had a temperature of 60 F. In the upperstove 5 of the furnace' it was heated to a maximum temperature of10001600 F., and was cooled to approximately 260 F. in passage throughthe lower stove 4 of the furnace. Ore was discharged, at 3, at the rateof 23.82 l.t./hr. and-at the discharge temperature of 260 F. j

It is of interest that of the total gas blown into the reducing roastingfurnace approximately 65% was int'i-duced, into the ore column, adjacentthe reduced ore product discharge 3 to cool the descending (hot) oredown to an exit temperature of approximately 260 F. Even at thisrelativelyV low temperature there was some danger of reoxidizing themagnetite formed from the hematite in the roasting operation.Consequently, .the

12 rateof.dischargethrough 3 was controlled by means of.Y astar gate andthe material was discharged under waterv in a spiral type classifier.

All of the heat to the system was supplied by burning 5I fuel4 oil inthe dutch oven combustion chambers 16 within theb mixing chambers (one,only, of which has been indicated inl the flow sheet). The procedure inburning vthefuel oil with no excess of oxygen made it possible to burnthe oil completely and elfectivelyjand to reduce radiation losses.

The quenched discharged ore from 3 was ground, in

a 9 ft. by 12 ft. ball mill to all minus Y1,00 mesh, and` then wasconcentrated magnetically on three, three-drum rotary wet magneticseparators.

In this example, the starting material was ore identical in analysis,and structure, to that used in Example 1. The apparatus was essentiallythe same as that used in Example l, and the ore was charged to it at therate of 25.44 gross (long) tons per hour.

The blower 12 forced 869.8#/minute of cold, clean,

spent carrier gas through the cold gas conduit 13. gas had the followingamounts and composition: l

#/min. Percent` Co 74.8 48.8 Co 4.3 0.5 H2-.- 1.7 0.2 H20 15.7 1.8 N2..773.3 88.9

Reducing gas, made in a Wellman-Galusha type of gas producer using coalas a fuel, was forced through conduit 1. This gas had the followingcomposition:

#/mln. Percent oo 0. 62 3.0 00.--- 4. 87 30.4 Hz.- 1.89 11.8 H10 0.291.8 N1- 8.35 52.1

The re-circulating carrier gas was split into two parts.

One part was diverted to conduit 15 and the residual part into conduit14. The gas in conduits 14 and 15 had the following composition andvolumes:

Conduit 15, #/min.

Conduit 14, #/mln.

Percent `The carrier gas from conduit 14 and the reducing from conduit 1commingled in conduit 2 to produceag 13 enriched Carrier 82S 0f thefollowing amount and com-v position: Y

. This enriched carrier gas" entered the YcireV column in lower stove 4where it recovered heat from the ore and ascended i'ntoY the upper orecolumn (stoveS). As it entered, it commingled with the gas from mixingchamber 17. This mixture of gases had the following'amount andcomposition: v

#/min. Percent CO 96. 5 i 9. CO 9. 7 0. Ha 3. 7 V0. N n- 895. 8 87. H2022. 3 Y2.

In order to keep the system from increasing in pressure, the vent 9 wasused to keep the system in balance. The minimum top gas waste toatmosphere Was 5.8% based on a nitrogen balance. This percentage wouldvary with temperature, moisture content, and CO content.

The remainder of the spent gases passed into wet dust collector-scrubber7 Where they were cooled and the excess moisture was condensed out andexpelled together with the excess CO2 over and beyond that accumulatingin the system for equilibrium while maintaining a nitrogen balance.

The amount and composition of these top gases, prior to venting, were asfollows:

#/min. Percent 0f these gases 7.5% exited through the vent (conduit 9)and 88.4% passed to the scrubber 7 (conduit 10).

The heat requirements of the above system were such that 201,000B.t.u./min. were required to heat theV ore from 60 F. to 1,000 F.;67,000 B.t.u./min. were required to evaporate the moisture and todehydrate the ore; and 10,000 B.t.u./min. were needed to meet radiationlosses for a total of 278,000 B.t.u./min.

The heat sources were: 31,000 B.t.u./min. from the exothermic reaction;160,000 B.t.u./min. were recovered by the ascending gases; and 87,000B.t.u./min. were supplied by combustion of fuel oil at the combustionchamber.

The heat losses from the reducing furnace were:

B.t.u./min. Radiation 10,000 Heat in rejected ore 41,000

Heat in top gases of which 67,000 is for dehydration of ore tei-nutonswas groundedin a ball mill to all minus mesh, and was then concentratedmagnetically on a series of three three-drum rotary wet magneticseparators.

I claim: y

1. Cyclical process of reductively roasting a ferruginous ore materialto convert the iron content thereof to magnetite, which comprisesestablishing a gravitationally descending column of the initiallysubstantially unheated ore material in particulate form, removingroasted ore material 'from the bottom of the column and adding freshv lore` material to be roasted onto the top of the column to maintain thelatters height, introducing into and counter# currently passing throughthe column from substantially the bottom to the top thereof a reactivegas mixture, initially at about room temperature, containing carbondioxide, inert gases and a gaseous active reducing agent selected fromthe group consisting of hydrogen, carbon monoxide and a mixture ofhydrogen and carbon monoxide, there being present substantially morecarbon dioxide than gaseous active reducing agent, introducing into thecolumn, at a level intermediate the top and the bottom of the same andsubstantially above the level of introduction of the reactive gasmixture, and countercurrently passing through the remainder of thecolumn a substantially inert, non-oxiding, heating gas mixturecomprising hot gaseous products of the combustion of a fluid fuel inair, said heating gas mixture being introduced at such an elevatedtemperature and in such a volume as to maintain the ore in a maxiumtemperature zone in the upper part of the column 'at a temperature offrom about 800 F. to about 1,700 F., cleaning and cooling a substantialpart of the spent gas mixture issuing from the top of the charge column,adding to a portion of the same a gas rich in said gaseous activereducing agent in an amount to reconstitute the aforesaid reactive gasmixture in composition and in volume, using the latter as the reactivegas mixture in continuation of the process, burning a duid carbonaceousfuel in an amount of air just sufcient to convert the combustiblecontent of the fuel to CO2, mixing with the resulting hot gaseouscombustion products a further portion of the cleaned and cooled spentgas mixture in an amount to reconstitute said heating gas mixture, usingthe resulting hot gas mixture as the substantially inert, non-oxidingheating as mixture in continuation of the process, and maintaining thevolume of circulating gases substantially constant by diverting a minorpart of said spent gas mixture from the cycle.

2. ln a cyclical process of reductively roasting an initiallysubstantially non-magnetic iron ore material, Whereby to convert theoxidic iron content thereof to magnetite, in a substantially gas-tightshaft type furnace, by countercurrent circulation, through at least apart of a gravitationally descending column of the ore material, of acurrent of a gas mixture containing no free oxygen and consistingessentially of a mixture of relatively inert gases including carbondioxide and a relatively active reducing gas selected from the groupconsisting of carbon dioxide, hydrogen and a mixture of carbon dioxideand hydrogen, in which gas mixture the content of carbon dioxide isseveral times the content of active reducing gas, which current of gasmixture after each passage through the ore material is deficient inactive reducing gas and contains moisture vapor and an enhanced contentof carbon dioxin a repetition of the cycle, the improvementvvhich con?Ysists in splitting the scrubbed gas mixture into'two unequal portions,to the relatively cold larger portion there being added an amount ofrelatively cold active reducing gas equivalent to that which in thecountercurrent passage through the ore column had` been oxidized, and tothe smaller portion there being added a hot, substantially neutralnon-oxidizing gas mixture at a temperature suf: iyciently elevated toraisethe temperature of the resulting heating gas mixture of scrubbedrecirculated gas and hot gas' mixture to within the range 800-1700 F.,and introducing said relatively cold enriched gas portion into'thecolumn of orematerial adjacent the bottom of the latter forcountercurrent passage through said column `and introducing said heatinggas mixture into s'a'id column of ore material at a level intermediatethe bottom and the top of said column for countercurrent passage throughthe upper part only of said column.,

3. The improved cyclicaly process defined in claim 2, in Which theactive reducing gas is a mixtur'ef o'f fhydrgen and carbon dioxide. 4.The improved cyclical process defined in claim 2, in which said enrichedgas mixture has the'approximate composition: i

Percent N2 8.8.0, COZ 8.5 CO v 1.2 H5 0.5 H2O 1;8

proximate composition:

Percent N2 87.1 CO2 9.4 CO 0.9 H2 0.4 HzQ 2-2 References Cited in the leof this patent UNITED STATES PATENTS 1,645,968 Percy Oct. 18, 19272,528,552 Royster Nov. 7, 1950 2,528,553 Royster Nov. 7, 1950 2,670,946Royster Mar. 2, 1954 2,676,095 De Vaney et a1 Apr. 20, 1954 2,717,205Edwards Sept. 6, 1955 UNTED STATES PATENT OFFICE CERTIFTCATE OFCORRECTION Paten Noo 2R93lv720 April 5Q 1960 Fred Da De Vaney It ishereby certified that error appears in the -prnted specification of theabove numbered patent requiring correction and that the said LettersPatent should read as corrected below.

Column lLl lines 37 and 56 :for "non-oxdng",xeaeh occurrencev readnon=oxdizng same column 14V lines 69 and 70U and column l59 line 24T!for "dioxde" each occurren( read monoxide --w Signed and sealed this27th day of September 1960.

(SEAL) Attest:

KARL H AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

1. CYCLICAL PROCESS OF REDUCTIVELY ROASTING A FERRUGINOUS ORE MATERIALTO CONVERT THE IRON CONTENT THEREOF TO MAGNETITE, WHICH COMPRISESESTABLISHING A GRAVITATIONALLY DESCENDING COLUMN OF THE INITIALLYSUBSTANTIALLY UNHEATED ORE MATERIAL IN PARTICULATE FORM, REMOVINGROASTED ORE MATERIAL FROM THE BOTTOM OF THE COLUMN AND ADDING FRESH OREMATERIAL TO BE ROASTED ONTO THE TOP OF THE COLUMN TO MAINTAIN THELATTER''S HEIGHT, INTRODUCING INTO AND COUNTERCURRENTLY PASSING THROUGHTHE COLUMN FROM SUBSTANTIALLY THE BOTTOM TO THE TOP THEREOF A REACTIVEGAS MIXTURE, INITIALLY AT ABOUT ROOM TEMPERATURE, CONTAINING CARBONDIOXIDE, INERT GASES AND A GASEOUS ACTIVE REDUCING AGENT SELECTED FROMTHE GROUP CONSISTING OF HYDROGEN, CARBON MONOXIDE AND A MIXTURE OFHYDROGEN AND CARBON MONOXIDE, THERE BEING PRESENT SUBSTANTIALLY MORECARBON DIOXIDE THAN GASEOUS ACTIVE REDUCING AGENT, INTRODUCING INTO THECOLUMN, AT A LEVEL INTERMEDIATE THE TOP AND THE BOTTOM OF THE SAME ANDSUBSTANTIALLY ABOVE THE LEVEL OF INTRODUCTION OF THE REACTIVE GASMIXTURE, AND COUNTERCURRENTLY PASSING THROUGH THE REMAINDER OF THECOLUMN A SUBSTANTIALLY INERT, NON-OXIDING, HEATING GAS MIXTURECOMPRISING HOT GASEOUS PRODUCTS OF THE COMBUSTION OF A FLUID FUEL INAIR, SAID HEATING GAS MIXTURE BEING INTRODUCED AT SUCH AN ELEVATEDTEMPERATURE AND IN SUCH A VOLUME AS TO MAINTAIN THE ORE IN A MAXIUMTEMPERATURE ZONE IN THE UPPER PART OF THE COLUMN AT A TEMPERATURE OFFROM ABOUT 800* F. TO ABOUT 1,700*F., CLEANING AND COOLING A SUBSTANTIALPART OF THE SPENT GAS MIXTURE ISSUING FROM THE TOP OF THE CHARGE COLUMN,ADDING TO A PORTION OF THE SAME A GAS RICH IN SAID GASEOUS ACTIVEREDUCING AGENT IN AN AMOUNT TO RECONSTITUTE THE AFORESAID REACTIVE GASMIXTURE IN COMPOSITION AND IN VOLUME, USING THE LATTER AS THE REACTIVEGAS MIXTURE IN CONTINUATION OF THE PROCESS, BURNING A FLUID CARBONACEOUSFUEL IN AN AMOUNT OF AIR JUST SURFICIENT TO CONVERT THE COBUSTIBLECONTENT OF THE FUEL TO CO2, MIXING WITH THE RESULTING HOT GASEOUSCOMBUSTION PRODUCTS A FURTHER PORTION OF THE CLEANED AND COOLED SPENTGAS MIXTURE IN AN AMOUNT TO RECONSTITUTE SAID HEATING GAS MIXTURE, USINGTHE RESULTING HOT GAS MIXTURE AS THE SUBSTANTIALLY INERT, NON-OXIDINGHEATING GAS MIXTURE IN CONTINUATION OF THE PROCESS, AND MAINTAINING THEVOLUME OF CIRCULATING GASES SUBSTANTIALLY CONSTANT BY DIVERTING A MINORPART OF SAID SPENT GAS MIXTURE FROM THE CYCLE.